Black Watch 25 Centre Console - Project Boat

Propellers play an extremely important role in a boat's performance. But with so many choices available nowadays, how do you know what prop is right for your boat?

Unfortunately, there is no easy answer. Most boat manufacturers or dealers should have a fair idea on what prop matches the boat and powerplant, however there is often room for improvement.

In the case of our Black Watch 25 project boat, there were no comparisons to go by. It was the first of these hulls to be fitted with twin 175hp Evinrude FICHT outboards, so prop selection was via a calculated guess.

We started with counter-rotating 17-inch OMC SST stainless propellers which turned out to be quite a good selection. During initial seatrials we clocked a top speed of 44kt which we were more than happy with.

After fishing the Black Watch at various tournaments up and down the east coast, we have realised that while acceleration and top speed are fine, the boat was not performing to its optimum in the 3000-4000 rev range.

While it would be nice to blast around the ocean at 40kt all the time, the fact of the matter is sea conditions rarely allow it. In rough conditions an 18-24kt cruise is more appropriate.

At 3000rpm the Black Watch was falling off the plane so we were constantly working the throttles to maintain a sensible cruise. The only problem is the throttle response of these big two-strokes are so sensitive that a little nudge and all of a sudden you are doing 30kt and 4000rpm. Not an ideal situation in three metres of sea.

Thus, we decided to do some prop testing to see if we could get the Black Watch to plane at 3000rpm without losing too much top speed.

Sydney's Pittwater was the venue for the prop testing and all figures are with four people and about 400lt of fuel onboard.

THE GPS DON'T LIE
<FIRST, p we ran original 17-inch SSTs and recorded the following figures (verified by BlueWater III?s Simrad EQ40 combination chartplotter sounder):

Note that at 3000rpm we were doing 13kt and still not planing, but at 4000rpm we were well and truly trucking at 29kt.

Next, we tried 17-inch OMC Vipers. The Viper is a three-bladed prop that has a longer tip and larger diameter than the SST. The Vipers recorded the following figures:

The Vipers got the Black Watch up and planing at 3000rpm, however the FICHTs were over-revving at Wide Open Throttle (WOT).

Not the ideal situation, but an improvement. Thus, we took the next step - that is, with good performance delivered by the 17-inch Vipers, perhaps the 19-inch Vipers might be the prop. It recorded the following figures:

The 19-inch Viper had all the characteristics of the ideal prop, however it was still over-revving a little at WOT. The top speed of 45.5kt is the fastest the Black Watch has ever gone.

Although we had basically decided the boat needed a 19-inch prop, we trialled a four-bladed 17-inch OMC Renegade Offshore anyway. It recorded the following figures:

Again the 17-inch pitch of the Renegade saw the outboards over-revving at WOT. It was obvious a 19-inch prop was required, but the four-bladers showed promise. As well as a quicker holeshot (Ed: not that this thing is ever slow out of the water!) the extra stern lift had the boat on the verge of planing at the desired 3000rpm mark.

So on went the fifth set of props for the day - four-bladed 19-inch Renegade Offshores. They recorded the following figures:

As is sometimes the case with trial and error, it was certainly a case of leaving the best till last. The 19-inch Renegade Offshores did everything we wanted them to do.

Not only does the Black Watch now plane at 3000rpm, yielding a good heavy weather cruise of close to 18kt, but it's now possible to finetune the cruise speed right through from 3000rpm-WOT - where we have also gained 1.3kt.

This ability to finetune your cruising speed is paramount when covering long distances in less than perfect conditions. There are times when 18kt is perfect and 20kt is too fast. When you're constantly having to play with the throttle to keep yourself in the comfort zone, it can be both fatiguing and dangerous. The 19-inch Offshores will allow us to essentially dial in any cruise speed between 18-30kt-plus and should also show benefit in fuel economy.

Unfortunately, as this issue goes to press, we had not had a chance to confirm our test results in the real world - that is, offshore. The test set of props were, at the time, the only 19-inch Renegade Offshores in captivity and as such had to stay in Sydney, while BlueWater III headed north for a look at Townsville, the Whitsundays and a session on the Great Barrier Reef.

We missed out on using the 19-inchers during the Townsville Corolla Billfish Tournament, but (if everything goes to plan) the crew will be sampling their wares in the Whitsundays as this issue goes to press...

The difference between water and petrol
It's relatively simple... Outboards should be used on water - they shouldn't, however, be fed with it. It's bad enough spending a day alongside a boat which keeps catching fish when you're not getting a touch. It's even worse when halfway home the engines go into limp mode and all manner of alarms ring.

That's exactly what happened during BlueWater's ill-fated tilt at the Townsville GFC's Toyota Corolla Billfish Challenge 2000.

Day one saw BlueWater III streak ahead of the field from the bimini start then dive behind Jim Dalling's magnificent Reel Chase for the bash down to Morinda Shoal off Cape Bowling Green. We spent a rather rocky but improving day there watching Capt Calvin Tilley brain them upon Utopia. His team tagged 10 fish after towing BlueWater III around for six hours as a teaser!

The troubles started about halfway home. After trolling all day, yours truly hit the throttles for the trip home and was rewarded with plenty of white smoke and one engine that was misfiring - shaking like a dog divesting itself of a packet of Wilkinson Sword's finest.

We limped the 25nm-odd back to Townsville's Breakwater Marina (well, limped isn't exactly the right term, the engines were still happy to rev to 4000rpm - just under 30kt) and diagnosed the problem as water in the fuel.

How did we know? Apart from the FICHTs' alarms, upon draining the main underfloor Racors we could have made several (salty) cups of tea with the water that came out of each one. The engine-mounted spin-on filters were the same story.

We'd struck trouble with water in the fuel once before during BlueWater III's maiden tournament - this year's NSWGFA Interclub. At that stage we put the problem down to a bad load of fuel - something that happens from time to time especially, it seems, at marinas.

It was clear, however, the true cause was something to do with the set-up onboard.

It wasn't long before we narrowed down the culprit. Or to be accurate, the culprits. Water was making its way into the tank via the hullside breathers.

Our thanks go to the crew at Townsville Evinrude dealer Angus Smith Marine, for their fast action in getting us going again. Service manager Gary Lancashire serviced the FICHTs quick smart (they were due anyway) and spent an afternoon re-routing the breather system and fitting new units out of harm's way (Ed: fingers crossed) on the transom.

For the record Black Watch has already made the change to its production 25s.

While our magic props were in transit (see main story) and didn't make it north in time for our Townsville adventure, one of the things we did fit in preparation was a set of Talon Technology Navman F41 Digital Fuel Gauges.

More than just gauges, the F41s are also fuel flow meters and can deliver stats on instantaneous fuel usage, amount used, amount left, etc.

According to Talon's Chris Baird the $295 units are calibrated to plus or minus 5% out of the box. They comprise a sender unit which is cut into the fuel line (after the fuel filter) for each engine and a head unit (again one per engine) which sits in the dash.

The units were, by all accounts, straightforward to fit (thanks to the crew at Townsville's Breakwater Marina) apart from the idiosyncrasies of having to run everything under the floor of a centre-console boat.

I'm loath to start quoting lt/hr figures here as these will no doubt change when we fit the new wheels. Thus, there will be more on the results from these next issue.

At this stage we can say that at 27kt the gauges are registering around 30lt/hr per side - pretty impressive. But even I can't believe the lt/hr figures we're registering at troll speeds and I've seen the numbers with my own eyes...

Once we get the gauges calibrated and the new wheels fitted we should be able to quote real figures. Suffice it to say, the relative economy of the FICHTs takes some believing. Indeed, jokes I've made about driving to Lord Howe aren't that silly - weather permitting, of course.

As you will have read elsewhere this issue, BlueWater III performed perfectly in the Whitsundays. The next stop is the Great Barrier Reef for a spot of heavy-tackle stand-up... Now, that will be fun!

Update Snapshots
Loud and clear: We've had dramas radio-wise with bad reception from day one on VHF, and a 27meg unit that was unserviceable. It's a problem that's taken some time to sort out. The units themselves are not at fault and though GME was initially baffled it now appears it may be a case of a packing too many electrical goodies into too small a console. We'll keep you informed...

On the road: A big thumbs up for our Suburban tow vehicle and Mackay Trailer. The Mackay makes launching and retrieving an absolute snap and has been hassle-free with well over 20,000km on it already. The Suburban is bulletproof, but recently benefited from the addition of an alloy TJM bullbar and a set of sensational Hella Rallye 4000 spotlights.

Who needs telly: An A-plus report too for our Simrad electronics. The EQ40 combo unit we're using takes a little learning (some functions aren't intuitive) but its performance is stunning. The big screen is easy to read and the innovative system of pages makes it easy to customise and scroll between combination or individual function screens. More on this in the next couple of issues...

Teak on a trailerboat: Are we regretting fitting teak covering boards? Though the timberwork has been knocked about and stained by roadgrime (hardly a problem on a 50-footer) all it takes to bring it back to its best is a light sand. Therefore, the answer's no... It looks great and is somehow nicer to sit on and have around than just plain 'glass.

Everything in its place: There's no shortage of underfloor storage on this boat (buyers of later BW25s won't have as much as the builder has deleted some of the hatches). This surfeit of storage will have to be watched, as we've already started to collect gear onboard 'just in case'.

Where the action is: The nature of this boat is to fight fish from forward of amidships. As delivered, there was no padding on the coamings, but we have since fitted it all around (see Whitsunday pics this issue). One item that will need attention before long is the deck's non-skid.

Too many boatshows and too many people with hard-soled shoes have accelerated wear... A job for the Christmas break perhaps.